than any which astronomers have ever seen,
except only the comet of 1843. When at its nearest its nucleus was only
a sixth part of the sun's diameter from his surface. Thus the part of
the comet's orbit along which astronomers traced its motion was only a
small part at one end of an enormously long oval, and very slight errors
of observation were sufficient to produce very large errors in the
determination of the nature of the comet's orbit. Encke admitted that
the period might, so far as the comparatively imperfect observations
made in 1680 were concerned, be any whatever, from 805 years to many
millions of years, or even to infinity--that is, the comet might have a
path not re-entering into itself, but carrying the comet for ever away
from the sun after its one visit to our system.

[42] For a portion of the passages which I have quoted in this essay I
am indebted to Guillemin's 'Treatise on Comets,' a useful contribution
to the literature of the subject, though somewhat inadequate so far as
exposition is concerned.

[43] Something very similar happened only a few years ago, so that we
cannot afford to laugh too freely at the terrors of France in 1773. It
was reported during the winter of 1871-1872, that Plantamour, the Swiss
astronomer, had predicted the earth's destruction by a comet on August
12, 1872. Yet there was no other foundation for this rumour than the
fact that Plantamour, in a lecture upon comets and meteors, had stated
that the meteors seen on August 10, 11, and 12 are bodies following in
the track of a comet whose orbit passes very near to the earth's. It was
very certainly known to astronomers that there could be no present
danger of a collision with this comet, for the comet has a period of at
least 150 years, and had last passed close to the earth's orbit (not to
the earth herself, be it understood) in 1862. But it was useless to
point this out. Many people insisted on believing that on August 12,
1872, the earth would come into collision, possibly disastrous, with a
mighty comet, which Plantamour was said to have detected and to have
shown by a profound calculation to be rushing directly upon our
unfortunate earth.

[44] A rather amusing mistake was made by the stenographers of a New
York paper in reporting the above sentence, which I happened to quote in
a lecture upon Comets and Meteors. Instead of Paradise they wrote Paris.
Those acquainted with Pitman's system of short-hand, the one most
comm